Method for providing a heater roll fuser with improved release material

ABSTRACT

OFFSET OF TONER TO A HEATED FUSING ROLL IS PREVENTED BY COATING THE FUSING ROLL WITH AN ADHESION PREVENTING LAYER OF AN IMMISCIBLE DISPERSION OF A HIGH VISCOSITY, LOW SURFACE TENSION COMPONENT SUCH AS ZINC OR ALUMINUM STEARATE OR BEHENATE AND LOW VISCOSITY, LOW SURFACE TENSION COMPONENT SUCH AS 50 CS. SILICONE OIL.

y 1974 B. R. BANKS E AL 3,810,776

METHOD FUR PROVIDING A HEATER ROLL FUSER WITH IMPROVED RELEASE MATERIAL Filed June 30, 1972 Ill/Willi.

US. Cl. 117-21 8 Claims ABSTRACT OF THE DISCLOSURE Offset of toner to a heated fusing roll is prevented by coating the fusing roll with an adhesion preventing layer of an immiscible dispersion of a. high viscosity, low surface tension component such as zinc or aluminum stearate or behenate and low viscosity, low surface tension component such as 50 cs. silicone oil.

BACKGROUND OF THE INVENTION Contact fusing of thermoplastic powder xerographic images is quite eificient both from the standpoint of power consumption and fusing speed. A typical contact fuser comprises a heated roll that conducts heat through its outer surface to a thermoplastic image held in contact therewith by a back-up or pressure roll. The heated image particles soften and flow into more intimate relation with the sheet upon which they are supported thus fixing the image. One or both of the rolls may have a deformable surface to provide a controllable residence time which the heat transferred to the thermoplastic image can be regulated. It has been found that the tendency of toner to transfer or offset onto the heated fusing roll is in good part determined by the degree of heating of the toner particles. Ideally the toner particles of the image coalesce and form a viscous liquid that will remain attached to the support sheet. Insuflicient heating leaves the toner particles in a partially powder form so that they can separate with part of the particles going to the heated roll and part of the particles remaining on the support sheet. On the other hand, excessive heating of the toner produces a liquid having low cohesive strength such that it tends to separate with the result again being the transfer of some toner to the heated fusing roll. The tendency for an offset or sticking failure can be reduced by minimizing the adhesive nature of the heated fusing roll.

It has been proposed to employ fusing rolls having surfaces of a material such as polytetrafluoroethylene and silicone polymers and elastomers which are known to have low surface free energy, either alone or in combination with lubricant liquids such as silicone oil to provide such a non-adhesive surface. While such materials do provide a relatively non-adhesive surface, they also create certain limitations on the overall performance of the contact fuser. For example, the operative life of a fusing roll having a permanent offset preventing or release surface layer will be limited by the life of that layer. Furthermore, those materials that are presently known to have good non-adhesive characteristics also tend to have relatively poor heat transfer properties. Thus the release surface layer represents an inhibiting factor in the transfer of heat from within the hot roll to its surface.

United States Patent O ice Heat transfer interference makes accurate surface temperature control more difiicult. External heating of such rolls has been proposed, however there remains the chiliculty of evenly distributing the heat through the surface of a poor heat conductor.

An object of our invention has thus been to devise a roll fuser that is not dependent upon a specific fusing roll surface material for its non-adhesion characteristics.

Another object of our invention has been to devise a roll fusing system employing a highly eflicient plain metal fusing roll.

DISCLOSURE OF THE INVENTION We have discovered that a stable offset preventing release layer can be generated and maintained on the surface of a heated fusing roll by mixing a dispersion of immiscible low surface tension liquids, including one liquid having a relatively high viscosity and the other having a relatively low viscosity. This layer is much thinner than any solid or permanent layer having a reasonably useful life and it does not impair the life of the roll to which it is applied. With our release layer it becomes possible to select the roll material for its longevity and heat transfer properties without compromise due to questions of offset prevention or sticking.

The particular liquids to be employed in our release layer must be selected with reference to the operating temperature of the heated roll. Xerographic toners fuse vw'thin a temperature range depending upon their resin constituents and the particular fusing system employed. While the currently popular toners are based on resins which are fused by existing contact fusing systems in the range of 175 C. to 220 C., it is conceivable that toners fusing much closer to room temperature could be usefully employed. Toners having too low a fusing temperature will smear and stick when handled at room temperature and thus are to be avoided. Since our system preferably employs a thermally conductive fusing roll, the surface temperature of the roll can be lowered somewhat from that used in a system having a partially insulated fusing roll. In fact, we prefer to use a fusing roll temperature of about C. with currently popular toners. Having determined a surface temperature for the fusing roll, the high and low viscosity liquids are selected for their properties at that surface temperature. Desirable properties are low surface tension with respect to liquid or solid toner, chemical stability, viscosity, and immiscibility with each other and with liquified toner. It is useful if at least one of the constituents is solid at room temperature so that the liquid can be dispensed from an easily handled block by a simple progressive melting operation.

We have had particularly satisfactory results by selecting either zinc stearate or zinc behenate on an aluminum roll to form the high viscosity constituent of our release coating and further by selecting 50 cs. silicone oil as the low viscosity constituent. The zinc stearate of zinc behenate both are solids at room temperature and adsorb the silicone oil to form a soap-like cake that is easily handled and can be dispensed by a heated spreading roll that simply melts its edge portion.

Dispensing of the release material by progressive melting of a solid cake is most easily accomplished where the solid component has a relatively sharp or distinct melting temperature. Fortunately the fatty acid salts of zinc have such distinct melting temperatures and thus are preferred by us.

While metallic soaps such as zinc stearate and zinc behenate have been used in the past as mold release agents due to their lubricity and elevated temperature stability properties, our experiments have been unsuccessful in using these materials alone as a release coating. Similarly, silicone oils have been used as mold release agents and roll release agents. Alone, however, silicone oils have proven unsatisfactory as a total release system. Unexpectedly we have discovered that the combination of these materials has proven to be quite satisfactory.

While the mechanism by which our coating operates is not completely understood, it is believed that the high viscosity liquid contributes stability to the coating that supports the low viscosity liquid uniformly over the fusing surface. It also provides an impenetrable barrier over the metal surface of the roll. The low viscosity liquid provides a barrier layer to separate the toner from the roll surface and from the high viscosity liquid. While the low viscosity liquid might be penetrated locally by toner globules, the low surface tension of the high viscosity material will negate any tendency of the toner to wet or spread over the surface of the high viscosity liquid as it would upon contacting a bare metal roll. The low viscosity barrier layer will wet the toner but because of its low, cohesive strength, it will tend to fracture and separate from the roll rather than cause toner to separate from the image. The stabilizing behavior of the high viscosity liquid is significantly enhanced where either a chemical reaction or polar attraction exists between the fusing roll surface and the high viscosity liquid. Such a reaction or attraction exists where a monocarboxylic or so-called fatty acid or metallic soap is applied to reactive metal surfaces such as zinc or aluminum. Only saturated monocarboxylic acids and their soap derivatives have been found to be useful in this regard.

The apparatus and method invention will be more completely understood by the following detail description of a specific preferred illustrative embodiment wherein reference is made to the accompanying drawings of which:

FIG. 1 is an outline elevational view of a xerographic type copy machine including a roll fuser constructed in accordance with our invention;

FIG. 2 is an enlarged elevational cross-sectional view of the roll fuser shown in FIG. 1; and

FIG. 3 is a fragmentary cross-sectional elevational view of the bearing structure used in the roll fuser shown in FIGS. 1 and 2.

More specifically in FIG. 1 there is shown a xerographictype copy machine having a copy drum 11 like that described in US. Pat. 3,5 88,242. Positioned about the copy drum 11 is a charging station 12 followed by an imaging station 13 at which a light image of a document on an exposure plane 14 is focused by lens 15 to imagewise discharge a photoconductive surface on the drum 11. A latent electrostatic image thus formed is developed by a cascade developer 16 in which a thermoplastic toner particle image is deposited upon the surface of the drum 11. Base sheet material such as paper 21 is fed and severed into sheets by knife 17 from a supply roll 22 prior to being delivered to a transfer station 18 at which the toner particle image 20 is deposited thereon. The paper 21 bearing the toner image 20 then is transmitted to a contact heat fuser or fixing station 30 while the photoconductor on drum 11 is passed to a cleaning station 19 preparatory to a further copy operation.

As is better shown in FIG. 2, the fixing station 30 comprises a heated fusing roll 31 and a backup or pressure roll 32 which together form a roll couple 33. Fusing roll 31 preferably includes a thin, but substantially rigid, metal cylindrical heat transfer wall 34 having a polished outer fusing surface 35. Fusing roll 31 is rotatably 4 mounted by bearings 40, one of which is shown in FIG. 3. A drive belt 41 connects fusing roll 31 to a motor or similar source of rotary motion 42. The bearing 40 includes a frame mounted inner race 43 that supports an outer race 44 upon which end walls 36 of the fusing roll 31 are mounted. A pulley 45 also is mounted on the outer race 44 for delivering rotary motion to the fusing roll 31 via the belt 41. The inner race 43 also supports suitable sockets 46 for supporting an infrared heat lamp 47 coaxially within the fusing roll 31. In operation the metal cylinder wall 34 provides an efiicient heat conducting path from lamp 47 to the fusing surface 35. It will be understood that the specific bearing structure and the heater mounting structure can be varied without departing from the concepts of our invention.

The back-up or pressure roll 32 is rotatably supported on arms 50 which are pivoted by shaft 51 to the machine frame. A cam device 52 is operable to raise the pressure roll 32 into pressure engagement with the fusing roll 31 to press sheet 21 thereagainst. The roll 32 includes a relatively thick outer surface layer 37 preferably of a material duch as a silicone elastomer which deforms under pressure to provide a footprint or nip 38 that is controllable to define the residence time of paper 21 against the fusing roll 31 for a given roll surface speed.

The release coating 70 of our invention is applied to the outer surface 35 of the fusing roll 31 by a spreader roll 60 that is supported by shaft 61 in rolling contact with the fusing roll 31. The spreader roll 60 may be heated separately from the fusing roll 31 or may be heated as shown simply by its contact with the fusing roll 31. Adjacent the spreader roll 60 is a dispensing device 62 for applying a thin layer of material 71 to the spreader roll surface The dispensing device 62 comprises a stationary tray 63 that slidably supports a pusher block 64 that is connected through a cable 65 to a spring motor 66. A pair of hold down rolls 67 are supported above the tray 63. Since in the preferred embodiment of our release coating, at least one of the components is a solid at room temperature, this solid material is for-med into a soap-like block 72 that is received by the pusher block 64 and is guided by hold down rolls 67 to be ablatively dispensed to spreader roll 60 during rotation thereof. As shown in FIG. 2 it is preferred that the dispensing device 62 be located relative to the direction of rotation of the spreader roll 60 to provide a maximum dwell time of material 71 on the spreader roll 60 prior to application to the heated roll 31.

From the foregoing it will be seen that toner images 20 carried by paper 21 from the drum 11 to the nip 38 of the roll couple 33 will be directly heated by contact with the coated surface 35 of fusing roll 31 and thereby fused by heat conducted thereto. As explained above, the coating 70 on fusing roll 31 will minimize or completely eliminate any tendency for toner to transfer or offset to the fusing roll 31 from the paper 21.

SELECTION OF MATERIALS The high viscosity liquid constituent to be employed in our coating should have the properties at temperatures suitable for fusing toners, of relatively low surface tension especially with respect to the toner to be fused chemical stability and a relatively high viscosity, for example about 300 cps. It should be substantially immiscible with the low viscosity component selected and with melted toner. It should also be colorless and non-toxic.

Additionally, for dispensing purposes, it is desirable but not mandatory that the high viscosity component be a solid at room temperature and have a well defined melt point. Also, the solid should be wettable by the low viscosity component, if it is liquid at room temperature, to enable a stable uniform room temperature mixture. Our preferred high viscosity constituents are shown in Table L 6 TABLE I EXAMPLES nia i iiir l 25 1?; A roll couple was constructed substantially as shown iacetergsion viscoglity Room in FIGS. 1-3 of the drawings incuding a 2 inch diameter Material Stable upto ig g: heated fusing roll with a inch wall thickness and a 71m qtemte 160 C v 19 300 8 rd 5 surface fimsh of 4-8 rms. The fusing roll wall was made p a s :1" 340 of either a high temperature aluminum alloy, zinc plated Aluminum stearate Unknown-..-.-..;....;-.. aluminum or gold plated copper to enable testing of alu- Mummum behelme I minum, zinc and gold surfaces.

I A 2000 watt heating lamp was supported within the .Pmduced as ammo layer by applying stem? i to an aluminum 1O fusing roll and was controlled to produce a fusion roll miLProduced as a mono layer by applying behcmc acid to an aluminum Surface temperature of about A 2% inch backup roll having a deformable silicone elastomer surface was Some other potentially suitable high viscosity compopressed against the fusing roll to provide a nip or footnents are: 2000 cs. silicone oil, 3060 Alta-Vis 1 oil, lithium print creating a dwell or residence time of 25-30 millistearate, 3:1 zinc stearate/lithium stearate mixture, zinc 15 seconds at a roll surface speed of 8-10 inches per seclaurate, zinc myristate, zinc palmitate, zinc lignocerate, ond. Paper strips 11 inches long bearing an unfused image zinc cerotate. including both line and half tone figures in the first three The low viscosity constituent of our release coating inches of their length were pasesd through the fusing nip. should have the properties at temperatures suitable for The data presented herein represents tests done on images fusing toner of low surface tension especially with respect composed of toner having a primary resin constituent of to the toner to be fused chemical stability and a relaa copolymer of n-butylmethacrylate and methylmethacrytively low viscosity, for example 10 cps. It should be sublate. Other less extensive tests employing a commercially stantially immiscible with the particular high viscosity available styrene based toner produced consistent results. constituent selected and melted toner. It should also be Each fused strip was examined to determine that acceptcolorless and non-toxic. Our preferred low viscosity conable fixing of the image had been accomplished. The blank stituent is 50 cs. silicone oil which has a surface tension trailing portion of the strip and the fusing roll were then at 150 C. of about 15 dynes/cm., a viscosity at 150 C. carefully examined for toner material offset from the of about 10 cps. and is substantially immiscible with image. In the following table, Examples 1 through 9, and liquid zinc behenate, zinc stearate, aluminum behenate 12 through 19 show tests where a dual liquid release layer and aluminum stearate and with liquid toner based on a was employed in accordance with our invention. Examples copolymer of n-butylmethacrylate and methylethacrylate. 10, 11 and 20 through 32 show tests involving release Other potentially suitable low viscosity components are: layers employing several of the components used to praclow viscosity white mineral oil, 210 Alta-Vis oil, and tice our invention but not combined in accordance with squalane (Hexamethyltetracosane). our novel method.

Example Material applied Roll surface Toner offset 1 3 parts zinc behenate, 1 part cs. silicone oil. No. 2. 8 parts zinc stearate, 1 part 50 cs. silicone 011.. No.

3. 3 parts zinc behenate, 1 part 50 cs. silicone oil. -No. 4. 3 parts zinc stearate, 1 part 50 cs. silicon oil- No. 5.. 3 parts zinc behenate, 1 part 50 cs. silicone oil- No, 6 3 parts zinc stearate, 1 part 50 cs. silicone oil.. N0. 7 3 parts stearic acid, 1 part 50 ca. silicone oil. No. 8 0 No. 9 3 parts behenic acid, 1 part 50 cs. silicone oil No, 10. 3 parts stearic acid, 1 part 50 cs. silicone 011.. Yes 11-.. 3 parts oleic acid, 1 part 50 cs. silicone oil A1uminum.-.. Yes. 12-.- 3 parts zinc stearate, 1 part white mineral oil 1 o.... 13. 3 parts zinc stearate, 1 part squalane 14. 3 paris 2 ,000 cs. silicone oil 1 part white mineral oil 15- o. 19. arts 3060 Alta-Vis 9 oil, 1 part 50 cs. silicone oil.. 1 o. 18... 3 parts 2,000 cs. silicone oil, 1 part white mineral oi 19-.. 3 parts 3060 Alta-Vie 1 oil, 1 part 50 cs. silicon 011.... 20.-. 50 cs. silicone oil 21 Zinc steamtn 22 -do 23 Behenic acid Aluminum.. Yes. 24... 2,000 cs. silicone oil Zinc Y 25-.. 1 part 50 cs. silicone oil, 1 part while mineral oil Aluminum...- Yes. 26... 3 parts 2,000 cs. silicone oil, 1 part 50 cs. silicone oil 3 pasts 2,000 cs. silicone oil, 1 part Acrawax O 3 war 3 parts oleic acid, 1 part 50 cs. silicone oil... 3 parts 2,000 cs. silicone oil, 1 part oleic acid- 1 Viscosity at 40IC. of 73 05.; at 100 O. of 8 cs. 9 Product of Standard Oil Co. of California.

a Product of Glyco Chemicals Inc. 4 Multiple tests were inconsistent. Some tests showed no oflset but were believed to be invalid due to roll contamination.

As stated above, it is preferred but not essential to em- Examples 1 and 2 represent the preferred implementaploy a roll surface having chemically reactivity or polar tion of our invention. When the materials listed were ap- 1 Product of Standard Oil Co. of California.

plied through a spreading roll as shown in the drawings, the average consumption rates of the release layer material was respectively for Example 1, 2-8 mg. and for Example 2, 8-20 mg. per 8 /2" x 11" copy. In these examples, as well as the remaining examples, the release material was detectable on the resultant copy but was of such a small amount as to not be considered objectionable. Examples 3 and 4 are similar to Examples 1 and 2 but with a zinc surface roll. The zinc roll surface appears to be less durable than the aluminum roll. Examples 5 and 6 are similar to Examples 1 and 2 but with a gold surface roll.

Examples 7 and 8 employed the application of stearic acid and 50 centistoke silicone oil respectively to aluminum and zinc fusing rolls. Example '9 is similar but with behenic acid. Stearic and behenic acids themselves do not possess the properties required of the high viscosity liquid component, however, a pseudo surface reaction is believed to occur with the aluminum or zinc roll surface to cause the generation of a monolayer of liquid aluminum or zinc stearic on the roll surface. This pseudo reaction thus creates the requisite high viscosity liquid component required for the successful practice of our invention. Compare with the successful results of Examples 7, 8, and 9, the unsuccessful results of Example 10 where an unreactive gold roll was employed. Also compare the unsuccessful result of Example 11 where oleic acid, an unsaturated fatty acid, was attempted in place of the saturated stearic and behenic acids.

Examples 12, 13, 14 and 15 show the successful performance of our method with low viscosity components other than the 50 centistokes silicone oil which we prefer.

Examples 14, 15, 16, 17, 18 and 19 show the successful performance of our method through the use of nonmetallic-soap, high viscosity components in the release layer. Example 17 shows the successful performance of our method with a release layer employing an inert gold roll with a non metatllic soap, high viscosity silicone oil combined with a non-silicone oil, low viscosity component to illustrate the breadth of our invention method.

Our experience has shown that while offset can be prevented with any of the variety of combinations of materials indicated in the examples showing no offset, our preferred embodiment of Examples 1 and 2 appear to be significantly easier to control and to provide stable operation over a wider range-of secondary operating conditions.

To verify our beliefs as to the criteria required for suc cessful performance of our method, our examples have included tests performed on materials not meeting that criteria. Examples 20, 21 and 22 show our unsuccessful attempt to use either the 50 centistoke silicone oil or zinc stearate separately as a release layer even though these components together make up the preferred embodiment of Example 2. Example 23 shows our unsuccessful attempt to use behenic acid alone or an aluminum roll even though Example 9 shows it successful performance in combination with the 50 cs. silicone oil. Example 24 shows our unsuccessful attempt to use the 2000 centistoke silicone oil alone as a release layer although this material is suitable as the high viscosity component for practicing our invention as illustrated by Examples 14, 15 and 18. Example 25 shows our unsuccessful attempt to make a dual component release layer of two low viscosity liquids even though these liquids are individually successfully employed as the low viscosity liquid in Examples 7 and 12. Example 2 6 shows our unsuccessful attempt to employ miscible high and low viscosity components even though these components individually serve satisfactorily when combined with other materials with which they are immiscible. Examples 27 and 28 show the unsuccessful attempt to employ Acrawax C wax as either the high viscosity or the low viscosity component of our invention even though this material is known to have antitack properties. Failure of Acrawax C wax to successfully perform is not fully understood but it is believed to be due to some tendency of it to react with the toner resin. Examples 11, 29, 30, 31 and 32 show our unsuccessful attempt to employ oleic acid alone or in combination with other suitable constituents to provide a successful release layer in accordance with our invention. While oleic acid falls within the class of monocarboxylic acids, it is unsaturated since there exists at least one double bond in the non-carboxylic portion of molecule. Thus, oleic acid tends to be more reactive than the saturated monoearboxylic acids.

It will be appreciated by those skilled in the art that we have discovered and developed a method for preventing toner offset in a contact fuser that enables the use of an efficient bare metal fusing'roll. The data we have presented herein demonstrates the breadth of our invention by a variety of examples showing both operative and inoperative situations involving variation of the materials applied to the heated roll and the heated roll material. While all possible materials falling within the scope of our invention have not been enumerated or demonstrated by examples, the number of examples will teach those skilled in the art sufficient basis by which other materials can be evaluated as possible candidates for implementation of our method. Having selected a possible candidate material, simple routine tests can demonstrate compatibility of that material with the various requirements of the system, all as illustrated by analogy in the foregoing specification.

It will be recognized that the apparatus shown in the drawing is not essential to our invention and that the various steps can be performed by different equipment. For example, release coatings involving liquid materials can be applied by a wick device in place of the ablating spreading roll shown.

In view of the foregoing, it will be seen that various modifications, additions, deletions can be made to our process and the apparatus disclosed without departing from the spirit and scope of our inventive concepts which are limited only by the appended claims.

We claim:

1. The method of operating a contact heat fuser having a fusing surface for fixing a toner image formed of thermoplastic toner to a base sheet comprising the steps of:

heating said surface to a temperature capable of fusing the toner image,

applying to said heated surface a thin layer of material to form a uniform release coating consisting essentially of a physical mixture of at least two primary immiscible low surface tension liquids that are both chemically stable at the temperature of said heated surface and are substantially immiscible with said toner material,

one of said liquids having a high viscosity and the other of said liquids having a relatively low viscosity at the temperature of said heated surface, and contacting the toner image carried on said base sheet with said heated coated surface for a period of time sufficient to fuse said toner image to said base sheet.

2. The method as defined in claim 1 wherein said applying step comprises:

providing a block of said material, and

progressively melting said block and delivering the material therefrom to said heated surface.

3. The method as defined in claim 2 wherein said block comprises a saturated fatty acid salt of zinc.

4. The method as defined in claim 3 wherein said other of said liquids comprises a low viscosity silicone oil that is intimately intermixed with and adsorbed on particles of said saturated fatty acid salt of zinc in said block.

5. The method as defined in claim 1 wherein said surface comprises, as a major component, a material selected from the class of zinc, aluminum. magnesium, nickel, copper, cadmium, iron, and alloys thereof and wherein:

the material applied to said surface comprises a substance selected from the class of saturated monocarboxylic acids and their derivatives for forming said high viscosity liquid.

6. The method as defined in claim 1 wherein said surface comprises, as a major component, a material selected from the class of zinc, aluminum, magnesium, nickel, copper, cadmium, iron, and alloys thereof and wherein:

the material applied to said surface comprises a substance selected from the class of saturated monocarboxylic acids and metallic soap derivatives thereof for forming said high viscosity liquid.

7. The method as defined in claim 1 wherein said surface comprises aluminum as a major component, and said applied material comprises a substance selected from the class of stearic acid, behenic acid, zinc stearate and zinc behenate.

8. The method as defined in claim 7 wherein said applied material further comprises a low viscosity silicone oil.

References Cited UNITED STATES PATENTS 3,268,351 8/1966 Van Dorn 117-21 3,324,791 6/ 1967 Cassano et a1. 100-172 3,449,548 6/1969 Adamek et a1. 219-216 15 3,612,820 10/1971 Punnett 219-216 10 3,666,247 5/1972 Banks 219-388 2,859,673 11/1958 HiX et a1. 118-637 3,291,466 12/1966 Aser et a1. 219-216 3,489,560 1/1970 Joseph 117-17.5 2,639,213 5/1953 Barth 117-106 R 3,186,855 6/1965 Miller 106-3823 OTHER REFERENCES IBM Technical Disclosure Bulletin, vol. 15, No. 3, p.

0 985, August 1972.

MICHAEL SOFOCLEOUS, Primary Examiner US. Cl. X.R. 

